JPS6126394A - Microphone device - Google Patents

Abstract

PURPOSE:To simplify the constitution of the doughnut directional microphone by fitting a differential-type microphone at the center of an acoustic tube so that a front part of a vibration film can point outside. CONSTITUTION:A differential-type microphone 4 is fitted at the center of an acoustic tube 5 so that a front part of a vibrating film can point outside. An acoustic path to a rear part of the vibrating film is constituted of the acoustic tube 5. The sound pressure applied to the front part of the differential-type microphone 4 becomes nondirectional, while the sound pressure applied to the rear part through the acoustic tube 5 becomes bidirectional in Y-Y'' axis direction. An output of the differential-type microphone 4 turns out to be a difference output between the sound pressure applied to the front part of the microphone 4 and that applied to the rear part of the microphone 4, and a doughnut-type directional pattern can be obtained as the result.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a microphone device having donut directivity suitable for conferences and the like.

Conventional configuration and its problems FIG. 1 shows a conventional microphone device.

The configuration of this conventional example will be explained below with reference to FIG. 1. In FIG. 1, 1 is a bidirectional microphone;
9. It is configured in the Y-Y' axis direction, 2 is an omnidirectional microphone, 3 is a differential circuit, and is configured to obtain the output difference between the microphones 1 and 2.

Next, the operation of the above conventional example will be explained. Figure 2 1'i
' FIG. 2 is an output turn diagram illustrating the operation of the microphone device in FIG. 1; In the figure, 1' indicates the output cover turn of the microphone 1, and 2' indicates the output cover turn of the microphone 2. In Figure 1, microphone 1
, 2, so 3'
An output pattern like this can be obtained. This is an output turn in the vertical plane, but since the outputs of microphones 1 and 2, turns 1' and 2', are the same in all vertical planes, the difference output pattern 8' is also It is the same in the vertical plane.In other words, it is a donut-like directional microphone device.

In addition to the configuration of this conventional example, it is also possible to arrange two unidirectional microphones coaxially in opposite directions to each other on the side 9 of the bidirectional microphone 1, and obtain the output difference between them.

Donut directional microphones are extremely suitable for conferences and the like because their horizontal pattern is non-directional and it is difficult to pick up unnecessary sound in the vertical axis direction.

However, in the above conventional configuration, multiple microphones are used and must be configured by combining them in a predetermined relationship, so the circuit configuration is complicated and many steps are required to obtain appropriate characteristics. It required an adjustment function and had various problems in terms of operability.

OBJECTS OF THE INVENTION The present invention eliminates the drawbacks of the above-mentioned conventional examples, and provides an excellent donut directional microphone device that can obtain suitable characteristics with a simple configuration and requires almost no adjustment function. The purpose is to

Structure of the Invention In order to achieve the above object, the present invention uses an acoustic tube, and installs a single differential microphone near the center of the acoustic tube so that the front part of the diaphragm faces outward. The acoustic path is effectively used to efficiently obtain the desired directivity.

DESCRIPTION OF EMBODIMENTS The configuration of an embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 is an external view of one embodiment of the microphone device of the present invention, in which 4 is a differential type microphone that allows sound to be introduced from the front and back of the diaphragm, and 5 is an open hole at both ends. It is an acoustic tube having a length L, which is the end 5', and several differential microphones 4 are installed approximately near the center thereof. FIG. 4 is a partially enlarged sectional view of the vicinity of the attachment of the differential microphone 4 in FIG. 3. In the figure, 4' indicates the position of the diaphragm, 4a the front part of the diaphragm 4', 4b the back of the diaphragm 4', and 6 the output lead of the differential microphone 4. That is, the differential microphone 4 is cut into several through holes formed near the center of the acoustic tube 5 so that the front part 4a of the diaphragm 4' is on the outside.
Direct sound is applied to the part a, and the sound tube 5 is arranged to act as a sound path to the back part 4b.

Next, the operation of the above embodiment will be explained. FIG. 5 is an explanatory diagram for explaining the operation. In the figure, t is the distance between the open end 5' of the acoustic tube 5 and the differential microphone 4, O is the sound introduction angle, and Po is Σjwt. indicates the sound pressure applied to the front portion 4a of the differential microphone 4. In the same figure, since Sin (90°-〇) = cos θ' -fi+, the sound pressure applied to the back 4bK of the differential microphone 4 from the Y direction is -c, ω-2πf, C: speed of sound, then p0Σj(wt+kl cose'-kl)
(It becomes 21, and similarly from the VCY' direction the back 4
The sound pressure applied to b is PoΣj (1 at wt-kl°0°θ-)
(3) becomes. Therefore, the composite sound pressure PT applied to the differential microphone 4 is given by the following equation.

In equation (4), the first item is the sound pressure applied to the front portion 4a of the differential microphone 4, which indicates that it is omnidirectional. The second item is the sound pressure applied to the back part 4b through the acoustic tube 5, and the sound pressure from each direction of 9, Y-Y'1 pongee becomes unidirectional ()--t shape), Since it is the difference output of each, it shows that it is bidirectional when synthesized. In other words, it shows that the directivity pattern is the same as that of the conventional microphone device shown in It can be seen that the equation (4) for calculating the sound pressure PT& is a donut directivity pattern.

FIG. 6 shows an example of frequency characteristics when L=40 cm and L=20 crn. It is clear from the figure that the reproduction band of the horizontal pattern (0°) is above the frequency where λ is approximately L-H (λ: wavelength of the sound wave). This is due to tube resonance of the acoustic tube 5. The characteristic in the 90° direction indicated by the dotted line in the figure has a donut directivity as can be seen from the figure.

In the case of Fig. 6, as mentioned above, the resonance of the Takumi sound tube 5 is affected by λ, especially at the frequency of L-2, the resonance Q
becomes high, and deterioration is seen in the frequency characteristics of the reproduction band.

FIG. 7 is a sectional view of a main part of another embodiment in which measures are taken to prevent such deterioration of frequency characteristics, and an acoustic resistance material 7 is attached near the open end 5' of the acoustic tube 5. ing. When the acoustic resistance material 7 is attached near the opening 5' in this way, the resonance Q is moderately lowered as shown in the frequency characteristics shown in FIG. 81, and deterioration of the frequency characteristics can be minimized.

Note that the Q of resonance can be sufficiently reduced by reducing the diameter of the acoustic tube 5.In addition, in the case of FIG. 6, the frequency characteristic diagram is approximately three times the frequency of L-2. A dip occurs and the frequency characteristics deteriorate. The cause of this appears to be due to the phase of the sound from each aperture end 5', but as a countermeasure to this problem, as shown in FIG. They may be slightly shifted in either direction along the axis, and the distances to the respective opening ends 5' may be made different from each other to make them asymmetrical. In this way, a frequency characteristic as shown in Fig. 10 is obtained, and the 6th
The tip around the frequency approximately three times the frequency corresponding to L-100 shown in the figure is greatly improved.

FIG. 11 shows still another embodiment, in which a plurality of sound holes 8 are provided between the mounting position of the differential microphone 4 and the open end 5' of the acoustic tube 5. . Therefore, in this case as well, the same effects as in the embodiment shown in FIG. 9 can be obtained.

That is, in the embodiment shown in FIG. 11, it is possible to obtain the frequency characteristics as shown in FIG. 12, and as in the embodiment shown in FIG. Nearby dips can be greatly improved.

In addition, if the incidence of sound from the front part 4a of the differential microphone 4 is eliminated by providing an appropriate air chamber, it is possible to make it a simple bidirectional microphone (Y-Y' axis direction). be. By using this and a unidirectional microphone to extract the output differentially, it is possible to obtain an MS (MAIN 5IDE) type microphone that also has a binaural effect. Also, the open end 5' of the acoustic tube 5
If it only goes in one direction, it can be made into a simple unidirectional microphone.In this case, if the incidence of sound from the front part 4a of the differential microphone 4 is eliminated by providing an appropriate air chamber, the It is also possible to reverse the direction of unidirectionality.

Effects of the Invention As is clear from the above-mentioned embodiments, the present invention has a differential microphone mounted in the center of the acoustic tube so that the front part of the diaphragm faces outward, and the entire acoustic path to the back of the diaphragm is constituted by the above-mentioned acoustic tube. It can be easily constructed using only an acoustic tube and a differential microphone, and it can easily obtain excellent frequency characteristics. It does not require many adjustment functions, and is of practical use. It is extremely advantageous.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a conventional microphone device, FIG. 2 is a rear cover diagram for explaining the operation of the microphone device, and FIG. 3 is an external view showing the configuration of an embodiment of the microphone device of the present invention. Figure 4 is an enlarged sectional view of the main part.
Fig. 5 is an explanatory diagram of the operation of the same embodiment, Fig. 6 is a frequency characteristic diagram of this embodiment, Fig. 7 is an enlarged sectional view of the main part of another embodiment, and Fig. 8 is a frequency characteristic diagram of the same embodiment. , FIG. 9 is an external view showing the configuration of yet another embodiment, FIG. 10 is a frequency characteristic diagram of the same embodiment, FIG. 11 is an external view showing the configuration of yet another embodiment, and FIG. The figure is a frequency characteristic diagram of the same embodiment. 4-. Differential microbond 5... Acoustic tube 5'... Open end 7... Acoustic resistance material. Name of agent: Patent attorney Toshio Nakao (1st person)
Figure (qo') ]Y Figure 5 5' Figure 6 Frequency (Hz) Figure 7 ゛Even' Figure 8 Frequency (Hz) Figure 9 Figure 1O Figure 11 Figure 12

Claims (4)

[Claims] (1) A through hole for mounting a differential microphone is formed near the center of the acoustic tube, at least one end of which is open, and the differential microphone is inserted into the through hole so that the front part of the diaphragm faces outward. A microphone device in which a microphone is attached to the diaphragm, and an acoustic path to the back of the diaphragm is formed by the acoustic tube. (2) The microphone device according to claim 1, wherein an acoustic resistance material is attached near the open end of the acoustic tube. (3) The microphone device according to claim 1, wherein the differential microphones are mounted at different distances from both ends of the acoustic tube. (4) The microphone device according to claim 1, wherein a plurality of sound holes are formed between the mounting position of the differential microphone and the open end of the acoustic tube.